Isaac slamming Gulf Coast with damaging floods, tornadoes

Slow-moving Tropical Storm Isaac continues to hammer coastal Louisiana, Mississippi, Alabama, and Florida's Panhandle with tornadoes, torrential rains, high winds, and a damaging storm surge. Over the past 24 hours, destructive tornadoes have touched down in Biloxi and Pascagoula, Mississippi, and one person was killed by a tree falling on a car in Pearl River County, Mississippi. A major flood event is occurring in Slidell, Louisiana, where Isaac's storm surge filled Bayou Bonfouca and the W-14 Canal, inundating portions of the city with 1 - 5 feet of water. While Isaac is now a weakening minimal-strength tropical storm, it is still a potent rainmaker, and will cause damaging floods all along its path for the next three days. Major river flooding is occurring or is about to occur on a number of rivers in the landfall area. In north central Tangipahoa Parish in southeast Louisiana and southwestern Pike County in southern Mississippi, a mandatory evacuation has been ordered for all low-lying areas and along the Tangipahoa River, due to the potential failure of the Lake Tangipahoa dam. Audubon Park in New Orleans, recorded 11.19" of rain as of 7 pm Wednesday night. An earlier amount of 19" was found to be erroneous, and this is not a 24-hour precipitation record for the city. According to wunderground's weather historian, Christopher C. Burt, New Orleans' greatest 24-hour rainfall on record is 14.01" on July 24 - 25, 1933. The Louisiana official state 24-hour record is 22.00" on Aug. 29, 1962 at Hakberry, although U.S. Army Corps of Engineers `Storm Studies' mentions a 23.80" falling in a 24-hour period at Millers Island during a TS on Aug 7-8, 1940. Storm total was 37.50" over a 60-hour period there during that event.

A few other rainfall totals from Isaac, through 11 am EDT on Thursday:

Isaac's storm surge winds downStorm surge levels along the coast of Mississippi and surrounding areas are gradually receding, and the surge has finally fallen below 5' at Waveland, which experienced a storm surge in excess of 5' for 36 hours. Isaac's storm surge levels were characteristic of a Category 2 hurricane, and lasted for an exceptionally long period of time. Waveland, Mississippi experienced a peak surge of 8' and peak storm tide of 9' (surge plus the natural high tide), which beat the levels that occurred during Category 2 Hurricane Gustav of 2008 (7' of storm tide.) The peak 11.06' storm surge at Shell Beach, which is in Lake Borgne, 30 miles southeast of New Orleans, exceeded the 9.5' surge recorded there during Gustav. According to an article in nola.com, Isaac pushed a storm surge of 13.6' into Lake Borgne, on the east side of New Orleans. This is not far from the 15.5' storm surge Hurricane Katrina brought to the location. It is quite possible that Isaac's storm surge might have breached levees of the east side of New Orleans, flooding areas inhabited by tens of thousands of people, had the Army Corps of Engineers not completed their $14.5 billion upgrade to the New Orleans flood defenses this year. I estimate that storm surge damage from Isaac will exceed $2 billion. Isaac has likely caused $2.5 billion in insured damage not related to flooding, insurance firm Eqecat estimated yesterday. Here were some of the peak storm surge values that were recorded at NOAA tide gauges during Isaac:

Figure 2. A TRMM satellite 3-D view of rainfall on Aug. 28 showed a few very powerful thunderstorms near Isaac's eye were reaching heights of almost 17 km (10.6 miles.) Intense bands of rain around Isaac were occasionally dropping rain at a rate of over 2.75 inches per hour. Image credit: SSAI/NASA, Hal Pierce.

Isaac's storm surge on the Mississippi RiverA storm surge estimated at 12' moved up the Mississippi in Plaquemines Parish near Port Sulphur, LA, near 8:30 pm EDT Tuesday, causing overtopping of the levees and flooding of homes in the mandatory evacuation areas behind the levees. These levees were not part of the $14.5 billion levee upgrade New Orleans got after Hurricane Katrina, and were not rated to Category 3 hurricane strength, like the levees protecting New Orleans are. Since salt water is more dense than fresh water, the surge travelled along the bottom of the river, with the fresh water flow of the river lying on top. The surge continued upriver, and before reaching New Orleans, encountered an underwater barrier in Plaquemines Parish. This barrier was constructed by the Army Corps of Engineers beginning on August 15, in order to keep salt water from moving upstream and contaminating drinking water for Plaquemines Parish and New Orleans. Salt water had made it 90 miles upriver to the outskirts of New Orleans, due to the low flow rate of the river (which had dropped 7' below average in height due to the drought of 2012.) According to a spokesperson for the National Weather Service River Forecast Office, this barrier was probably able to completely block the flow of salt water upriver due to Isaac's storm surge, and no salt water made it as far as New Orleans. However, the massive intrusion of ocean water into the river channel caused the mighty Mississippi's fresh water flow to back up for hundreds of miles. Water levels were elevated by 10' in New Orleans (103 miles upstream from the mouth of the Mississippi), 8' in Baton Rouge (228 miles upstream), and 1.4' at Knox Landing, an amazing 314 miles upstream.

Hurricane Kirk in the Central AtlanticHurricane Kirk intensified into a 75 mph Category 1 hurricane this morning, becoming the busy 2012 Atlantic hurricane season's fifth hurricane. With the season's mid-point of September 10 still almost 2 weeks away, we've already had 12 named storms and 5 hurricanes, which is close to what an entire season experiences in an average year (11 named storms and 6 hurricanes.) Kirk should stay well out to sea and not trouble any land areas.

Figure 3. Morning satellite image of Hurricane Kirk.

Tropical Storm Leslie forms in the Central AtlanticTropical Storm Leslie has formed in the Central Atlantic. Leslie's formation on August 30 puts 2012 in 2nd place for earliest formation date of the season's 12th storm. Only 1995 had an earlier formation date of the season's 12th storm. With records dating back to 1851, this year is only the second time 8 total storms have formed in August. The other year was 2004, when the first storm of the season formed on August 1 (Alex), and the 8th storm (Hermine)formed on August 29th. Leslie is organizing quickly, and appears destined to become a hurricane before the week is out. Fortunately, Hurricane Kirk is weakening the ridge of high pressure to the north of Leslie, and Leslie is expected to turn to the northwest and miss the Lesser Antilles Islands. In the long term, it remains unclear if Leslie will follow Kirk and fully recurve out to sea. The latest 2 runs of the GFS model have predicted that Leslie will recurve out to sea and not threaten any land areas, but the latest 2 runs of the ECMWF model have predicted that the trough of low pressure pulling Kirk to the northeast will not be strong enough to recurve Leslie out to sea. Instead, the ECMWF predicts that a ridge of high pressure will build in early next week, forcing Leslie more to the northwest, making the storm a potential threat to Bermuda, then to the Northeast U.S. and Canada in 8 - 11 days.

Quoting waterskiman:Yep it's not a bad store lots of bargans. I noticed they have changed some things that are now cheaper than dollar tree if you can believe that. Now if they could bake bread like publix It would be about perfect.

If I can ever figure how to get out of the store with all of the long ramps leading nowhere

Quoting PalmBeachWeather:waterski.... You have one of the best Winn Dixies I have ever been too near the hospital, Dillons, and my favorite Pier 1, That is my stop for my diving or fishing expiditions

Yep it's not a bad store lots of bargans. I noticed they have changed some things that are now cheaper than dollar tree if you can believe that. Now if they could bake bread like publix It would be about perfect.

Quoting AussieStorm:Tonights Barometer Bob Show is about to get underway. Topics will be, Hurricane Isaac, the Tropics, Storm Chasers that witnessed Isaac and his wrath will also be calling in.Plus, whats next?Join us in Storm Chat and watch the show at http://irc.barometerbob.net/I'm there.... will you???

During Hurricane Ike, Chrystal Beach, TX, I did a no-no. Didn't know MRE's had so many calories... several a day and kept getting pants tighter and tighter... finally read the labels. OOPS. Spam Lite would have been great there (I'm the only person in North America that really likes Spam).

Im not a fan of spam but I do like Treet..is there a difference? it comes in good during hurricanes..

Just in case you're wondering why Kirk's satellite intensity is low for such a structurally beautiful storm, this is what the Dvorak estimate sees. Look at how little deep convection there is.

Meanwhile, Leslie is looking fantastic. Her CDO has developed beautifully, and just for comparison, her deepest convection is at least 4 shades darker than Kirk's. Healthy ventilation on the entire western side of the storm and spiral banding evident on the east.

I'm thinking it could cross 20n around 60w, but that is just my opinion.

It seems possible, keep in mind the models and the nhc are going to need time to get a good handle on leslies track, this morning it was just a tropical wave, and tonight a tropical storm thats getting stronger, if it doesnt slow down, i think Antigua and Barbuda could have some tropical storm force winds!! Will see what happens with the ridge

During Hurricane Ike, Chrystal Beach, TX, I did a no-no. Didn't know MRE's had so many calories... several a day and kept getting pants tighter and tighter... finally read the labels. OOPS. Spam Lite would have been great there (I'm the only person in North America that really likes Spam).

Quoting mks:Thanks Grothar. Next question now, If Leslie misses the first weakness how much of a chance does she have of impacting the northeast Caribbean?

Every place but the Cayman Islands. :) At this point it really is too early to tell. The models have performed very well this year.

People talk about the models doing wind-shield wiper dances, but the atmosphere is always changing and the models change with them. We have all seen models 5 days out coming directly into the Caribbean and then turn North 800 miles out and vice-versa.

Tonights Barometer Bob Show is about to get underway. Topics will be, Hurricane Isaac, the Tropics, Storm Chasers that witnessed Isaac and his wrath will also be calling in.Plus, whats next?Join us in Storm Chat and watch the show at http://irc.barometerbob.net/I'm there.... will you???

Quoting mks:Thanks Grothar. Next question now, If Leslie misses the first weakness how much of a chance does she have of impacting the northeast Caribbean?

It should pull it poleward initially just enough to probably miss the NE fringes of the Caribbean by couple degrees. Chances of missing to the Caribbean is about 60% to 70% at the moment. keep an eye on it and watch the NHC adivories to see if anything changes.

During Hurricane Ike, Chrystal Beach, TX, I did a no-no. Didn't know MRE's had so many calories... several a day and kept getting pants tighter and tighter... finally read the labels. OOPS. Spam Lite would have been great there (I'm the only person in North America that really likes Spam).

Harry..............NO... I like Spam, fried with cheese melted on it and yellow mustard on a burger bun... Yummy

Quoting StormDrain:Been puzzling over this since Wednesday morning. Been looking at maps of the new ACE walls and of the River delta to try and understand. Isaac's angle of approach probably contributed but exactly how did it happen? (rhetorical ?)

The Plaquemines flooding, and the flooding on north shore of L. Pontchartrain. Residents of both areas were quoted over and over saying nothing like this happened with K storm or Gustav. The two police officers who went out to check Plaquemines east bank levee early Wednesday morning and had to be rescued when the flood advanced so quick they could not get out and had to be rescued - maybe they can shed some light on it. And I hope it is looked at in the post-season analysis when NHC has time to take a closer look.

image credit NASA

image credit: NOLA Army Corps of Engineers

Lower right: See Braithwaite. Dark green line along River is new wall on west bank. Gray line the east levee.

Stormdrain,This may have already been mentioned elsewhere.

If you wanted to pick a place on the River where a prolonged period of strong SE winds/surge in conjunction with a hurricane landfall could combine with a particular orientation of a protection levee (backlevee-not a mainline river levee) to over-top or breach a levee, you might not find a much better set-up. A funnel.

SIL and family live on the West Bank across from Braithwaite. They're here with us now. No power at the house. Semi-familiar with the area and similar issues in the past.

Quoting PalmBeachWeather:If you have never tried the "Spam Lite" in the light blue can, it isn't too bad.... During a catastrophe one still has to watch one's weight

During Hurricane Ike, Chrystal Beach, TX, I did a no-no. Didn't know MRE's had so many calories... several a day and kept getting pants tighter and tighter... finally read the labels. OOPS. Spam Lite would have been great there (I'm the only person in North America that really likes Spam).